Python Variables and Operators - Python and CSV Files

Python Variables and Operators - Python and CSV Files

Key features of Python:

·         It is a general purpose programming language which can be, used for both scientific and non-scientific programming.

·         It is a platform independent programming language.

·         The programs written in Python are easily readable and understandable.

 

Python Coding:

·         In Python, programs can be written in two ways namely Interactive mode and Script mode.

·         The Interactive mode allows us to write codes in Python command prompt ( > > >) whereas in script mode programs can be written and stored as separate file with the extension . py and executed.

·         Script mode is used to create and edit python source file.

Tokens.

Python breaks each logical line into a sequence of elementary lexical components known as Tokens.

The normal token types are

·         Identifiers

·         Keywords

·         Operators

·         Delimiters

·         Literals

 

Operators used in Python :

·         Arithmetic operators

·         Relational or Comparative operator

·         Logical operators

·         Assignment operators

·         Conditional operator

 

Input-output functions:

·         The input () function helps to enter data at run time by the user .

·         The output function print () is used to display the result of the program on the screen after execution.

 

Comment statement.:

# are considered as comments and ignored by the Python interpreter.

Python and CSV Files

SV file:

A CSV file is a human readable text file where each line has a number of fields, separated by commas or some other delimiter

Two ways to read a CSV file:

The two ways to read a CSV file are using csv.reader() function and using DictReader class.

Python File Modes :

 

Mode	Description
‘r’	Open a file for reading. (default)
‘w’	Open a file for writing. Creates a new file if it does not exist or truncates the file if it exists.
‘x’	Open a file for exclusive creation. If the file already exists, the operation fails.
‘a’	Open for appending at the end of the file without truncating it. Creates a new file if it does not exist.
‘t’	Open in text mode. (default)
‘b’	Open in binary mode.
‘+’	Open a file for updating (reading and writing)

 

The default mode of csv file in reading and writing is text mode

Binary mode can be used when dealing with non-text files like image or exe files.

Garbage collector:

Python has a garbage collector to clean up unreferenced objects

Skip initial space:

“skip initial space” is used for removing whitespaces after the delimiter

CSV library:

The CSV library contains objects and other code to read, write, and process data from and to CSV files.

csv.reader , csv.writer,csv.DictReader ,csv.DictWriter :

·         csv.reader and csv.writer work with list/tuple.

·         csv.DictReader and csv.DictWriter work with dictionary .

·         csv.DictReader and csv.DictWriter take additional argument fieldnames that are used as dictionary keys.

·         The csv.writer() method returns a writer object which converts the user’s data into delimited strings.

·         DictReader() class of csv module creates an object which maps data to a dictionary.

operator.itemgetter():

operator.itemgetter() can be used to sort by more than one column operator.itemgetter()

itemgetter():

itemgetter() with multiple indices is used to sort by more than one column.

writerow() Vs Writerows() :

The writerow() method writes one row at a time. Writerows() method is used to write all the data at once.

csv.register_dialect():

CSV file having custom delimiter is read with the help of csv.register_dialect().

close() method:

close() method will free up the resources that were tied with the file

Line Terminator:

A Line Terminator is a string used to terminate lines produced by writer.

Dialect :

A dialect is a class of csv module which helps to define parameters for reading and writing CSV.

Ordered Dict:

An Ordered Dict is a dictionary subclass which saves the order in which its contents are added.